1. Field of the Invention
The present invention relates to a vacuum regulating valve for regulating the pressure in an evacuated vacuum vessel for chemical reaction included in a physical or chemical machine or the like.
2. Description of Related Art
A chemical process, such as an etching process, is carried out in a vacuum vessel included in a semiconductor device fabricating system. The vacuum vessel is evacuated at a negative pressure by a vacuum pump. Such a pressure regulating valve is placed in an external line connecting the vacuum vessel to the vacuum pump and has two ports connected, respectively, to a vacuum vessel and a vacuum pump, internal passage connecting the two ports, a valve seat formed in the internal passage, a valve element to be seated on the valve seat to close the pressure regulating valve, and a valve element operating unit, such as one comprising a cylinder actuator, for moving the valve element onto and away from the valve seat to close and open the pressure regulating valve. The vacuum in the vacuum vessel is regulated by opening/closing the valve through the operation of the valve element operating unit.
For instance, in reducing the pressure in the vacuum vessel, for instance, fully opening the vacuum regulating valve to rapidly evacuate the vacuum vessel is likely to cause a large volume of the gas in the vessel to flow all at once which leads to an undesirable turbulence in the vacuum vessel and the external and internal passages, with stirring up particles in the vessel and passages. Therefore, there has been proposed an arrangement for improving the gas flow characteristics, as disclosed in JP-A-2001-263532 for instance, where a main fluid passage having a relatively large section area and a sub fluid passage having a relatively small section area are disposed in parallel in a vacuum regulating valve. In operation, the sub fluid passage is first opened to perform in an initial period of a vacuuming operation, and the main fluid passage is subsequently opened to perform the vacuuming operation in full.
However, the above conventional valve is somewhat complex in structure, since a sub valve mechanism for opening/closing the sub fluid passage having the relatively small cross section is dually disposed inside a valve element, a valve stem, a piston, etc. of a main valve mechanism for opening/closing the main fluid passage. Thus, there has been a request for a vacuum regulating valve which is simplified in structure.